Methods and apparatus for rejuvenation of amorphous alloys and micro-alloying

ABSTRACT

The disclosure provides a method of modifying a surface of a metallic glass. The method includes applying an electron beam within an energy band to a crystalline metal portion at a surface zone of the metallic glass. The method also includes changing the crystalline metal portion to an amorphous portion at the surface zone of the metallic glass, while a bulk region embedded in the metallic glass under the surface zone remains crystalline.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This patent application claims the benefit of U.S. patent application Ser. No. 62/394,070, entitled “METHODS AND APPARATUS FOR REJUVENATION OF AMORPHOUS ALLOYS AND MICRO-ALLOYING,” filed on Sep. 13, 2016 under 35 U.S.C. § 119(e), which is incorporated herein by reference in its entirety.

FIELD

The disclosure is directed to apparatuses and methods for surface modification by pulsed electron beam radiation.

BACKGROUND

Amorphous alloys have properties such as high corrosion resistance, high strength, and large elastic elongation. However, amorphous alloys are metastable phase materials, which can change from an amorphous structure towards a thermally stable structure under certain external factors, such as physical stress. The transition is a one-way reaction. When the amorphous structure makes the transition to become the thermally stable structure, such as a crystalline structure, structural relaxation occurs. Embrittlement is associated with the structural relaxation.

In some cases, plastic deformation can localize into a narrow band region at room temperature, resulting in sudden fracture, exhibiting almost no macroscopic plastic deformation under uniaxial tensile and compressive loadings. This brittle nature can limit the use of amorphous alloys as structural materials.

SUMMARY

In an embodiment, a method is provided for surface modification of a metallic glass. The method includes applying an electron beam within an energy band to a crystalline metal portion at the metallic glass surface. The method also includes changing the crystalline metal portion to an amorphous portion at a surface zone of the metallic glass surface, while a bulk region embedded in the metallic glass under the surface zone remains crystalline. The surface zone may have a depth up to 100 μm. In some variations, the depth of the surface zone can be greater than 100 μm. The surface zone may also have the same composition as the bulk region.

In an embodiment, a method is provided for micro-alloying an element on a metallic glass. The method may include sputtering a target material onto a surface of the metallic glass. The method may also include alloying the target material with the metallic glass to form an amorphous surface zone comprising the target material and the metallic glass. The surface zone may have a depth of up to 5 μm. The surface zone may also have a different composition from the metallic glass.

In an embodiment, a method is provided for surface modification of a metallic glass. The method may include applying an electron beam within an energy band to a localized crystalline metal portion within the surface of the metallic glass. The method may also include changing the localized crystalline metal portion at a surface zone of the metallic glass to an amorphous portion while a bulk region embedded in the metallic glass under the surface zone remains crystalline. The surface zone may have a depth of up to 5 μm.

Additional embodiments and features are set forth in part in the description that follows, and will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the disclosed subject matter. A further understanding of the nature and advantages of the disclosure may be realized by reference to the remaining portions of the specification and the drawings, which forms a part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be more fully understood with reference to the following figures and data graphs, which are presented as various embodiments of the disclosure and should not be construed as a complete recitation of the scope of the disclosure, wherein:

FIG. 1 illustrates a schematic for a conventional apparatus for pulsed electron beam radiation in accordance with embodiments of the disclosure.

FIG. 2 is an optical image that depicts a surface of a metallic glass including damage by a high intensity electron beam radiation in accordance with embodiments of the disclosure.

FIG. 3 illustrates a schematic for a modified apparatus for pulsed electron beam radiation in accordance with embodiments of the disclosure.

FIG. 4 illustrates a schematic configuration of a modified apparatus for pulsed electron beam radiation including electrically isolated metallic plates for sputtering and micro-alloying in accordance with embodiments of the disclosure.

FIG. 5 shows an optical photo of a modified metallic glass surface that has a slightly different compositional change due to micro-alloying from sputtered atoms by the pulsed electron beam radiation using the modified of FIG. 4 in accordance with embodiments of the disclosure.

FIG. 6A illustrates a micro-alloyed surface of Zr-based metallic glass in an embodiment of the disclosure.

FIG. 6B illustrates a rejuvenated surface structure on a crystalline metal portion in a metallic glass in an embodiment of the disclosure.

FIG. 7A is a schematic that illustrates an amorphous structure having a surface melted by an electron beam radiation in accordance with embodiments of the disclosure.

FIG. 7B is a schematic that illustrates the surface modification of the amorphous structure after rejuvenation by the electron beam in accordance with embodiments of the disclosure.

FIG. 8 shows X-ray diffraction patterns for a crystalline metal portion of a metallic glass prior to rejuvenation and an amorphous portion of the metallic glass after rejuvenation in an embodiment of the disclosure.

FIG. 9 is an optical image of a crystalline metal portion in a metallic glass prior to rejuvenation in an embodiment of the disclosure.

FIG. 10 is an optical image of a metallic glass including a rejuvenated amorphous portion and a crystalline metal portion after rejuvenation in an embodiment of the disclosure.

FIG. 11 depicts a portable electronic device having a metallic glass coating embedded therein.

DETAILED DESCRIPTION

The disclosure may be understood by reference to the following detailed description, taken in conjunction with the drawings as described below. It is noted that, for purposes of illustrative clarity, certain elements in various drawings may not be drawn to scale.

Because metallic glasses may crystallize due to mechanical stress, or reheating and slowly cooling, the disclosure is directed to methods of and an apparatus for modifying the surface of the metallic glass after crystallization. In some embodiments, the method may include applying an electron beam to a surface of crystalline metal portion within a metallic glass and rejuvenating the crystalline surface to become amorphous.

Rejuvenation is a process that can change a metastable phase (e.g. crystalline phase or structure) into an amorphous structure without changing the chemical composition of the metallic glass. Rejuvenation is accompanied by an increase in the enthalpy and free volume and is thus the inverse of aging.

In some embodiments, the method may include rejuvenating a surface of a metallic glass that has localized regions of crystalline portion within a metallic glass to become amorphous. The disclosure also provides a method for micro-alloying at least one element onto a metallic glass surface. The method may include sputtering a target material onto the surface of the metallic glass and micro-alloying the target material with the metallic glass and forming an amorphous surface region.

The disclosure also provides a modified pulsed electron beam radiation apparatus for achieving rejuvenation of a crystalline metal portion on a metallic glass using pulsed electron beam radiation. In some embodiments, the modified pulsed electron beam radiation apparatus includes a pulsed electron beam radiation apparatus and an energy filter for filtering electrons. The modified pulsed electron beam radiation apparatus can be used for surface modification, rework, or repair by healing the surface of the crystalline metal portion in a metallic glass, which may have structural relaxation or embrittlement.

The disclosure also provides a modified pulsed electron beam radiation apparatus for micro-alloying a surface of a metallic glass using pulsed electron beam radiation. In some embodiments, the modified pulsed electron beam radiation apparatus may include a sputtering capability for scattering a target material toward the surface of the metallic glass and micro-alloying the target material with the metallic glass to form an amorphous layer over the metallic glass.

FIG. 1 shows a conventional pulsed electron beam apparatus, which is a pulsed electron beam source or gun. As shown in FIG. 1, a conventional apparatus 100 includes a cathode 102, an anode 104, and a high voltage source 106 between the cathode 102 and anode 104 for producing high energy electrons in a vacuum chamber 110. The vacuum chamber 110 also includes an aperture 112 for outputting an electron beam. The pulsed electron beam radiation apparatus 100 also includes an electro-lens 108 for focusing an electron beam 114 and outputting the electron beam 114 through the aperture 112.

The electron beam 114 outputted through the aperture 112 is in a three-dimensional (3D) cone shape. In the conventional pulsed electron beam radiation apparatus 100, the electrons have a relatively broad energy band or energy distribution, i.e. the electrons have variations in energy. For example, some electrons may have higher energy than other electrons. The electron beam 114 has an electron energy distribution 122, which is the intensity I of the electrons versus energy E. As shown in FIG. 1, the electron energy distribution 122 may look like a bell curve, with a peak intensity 116 in the middle of the energy distribution, an extra high energy band 118 near the high energy end (e.g. to the right side of the peak intensity 116), and a low energy band 120 near the low energy end (e.g. to the left side of the peak intensity 116).

One of the drawbacks of the conventional pulsed electron beam radiation apparatus 100 is that the very high energy of the electron beam may damage a surface of a metallic glass. In some cases, the high energy electron beam in the conventional pulsed electron beam apparatus 100 can create a large hole on the surface of the metallic glass. FIG. 2 is an image that depicts a surface of a metallic glass after an accidental attack by high intensity electron beam radiation, such as from the electrons with energy in the extra high energy band 118. As shown in FIG. 2, a large hole 202 appears on the surface of a metallic glass 206. Also, a small hole 204 appears on the surface of the metallic glass 206.

The modified pulsed electron beam radiation apparatus disclosed herein can be used to modifying crystalline metal portions on the surface of the metallic glass. The apparatus can be used to apply an electron beam to a crystalline metal portion in a metallic glass surface, and rejuvenating the surface to become amorphous. In some embodiments, the apparatus can be used to rejuvenate localized crystalline metal portions to become amorphous. In other embodiments, the apparatus can be used to form an amorphous layer on crystalline metal portion in a metallic glass.

In some embodiments, the modified pulsed electron beam radiation includes a filter to reduce the power of the electron beam radiation. FIG. 3 illustrates a schematic for a modified apparatus for pulsed electron beam radiation in an embodiment. Modified pulsed electron beam radiation apparatus 300 includes a magnet 302 for changing the direction of the electron beam. The magnet 302 may be formed of a solenoid coil among others.

As shown in FIG. 3, an electron beam 304 passes through the aperture 112 of the conventional pulsed electron beam radiation apparatus 100. The magnet 302 can be used to change the orientation of the electron beam 304 to bend the electron beam 304 and to output a beam 306. For example, as illustrated in FIG. 3, the electron beam 304 impacts the magnet 302 and its orientation is rotated about 90°. Other orientations are possible, and the magnet can rotate the electron beam 304 range from 0 to 180°.

Initially, the electron beam 306 has the broad energy distribution 122 of the conventional pulsed electron beam radiation apparatus 100. However, the apparatus 300 includes an energy filter 308, such as a bending filter, for modifying the energy distribution. The energy filter 308 removes both the high energy electrons and the low energy electrons to output a filtered electron beam 310, which has a narrower modified energy distribution 312 than the energy distribution 122. The modified energy distribution 312 of the modified pulsed electron beam radiation apparatus 300 has a mean energy 316 and a width 314, which is smaller than the width 128 of the energy distribution 122 of the electron beam.

The modified energy distribution 312 of the output electron beam 310 can be controlled in the modified apparatus 300 by the filter 308. For example, the mean energy 316 and width 314 of the modified energy distribution 312 of the electron beam 310 may vary depending upon applications. In some embodiments, the electrons in both the extra high energy region 118 and the low energy region 116 are filtered by the filter 308. In some embodiments, the electrons in the extra high energy region 118 may be filtered out by using the filter in the modified apparatus 300, while the electrons in the low energy region 116 may not be filtered.

In some embodiments, the filter 308 may be a bent type filter. In alternative embodiments, other filters may be used to control the energy distribution of the electron beam. The filtered electron beam 310 may have a varying beam size, which may be controlled by the filter 308.

In another embodiment, a target material can be sputtered onto a specimen by the pulsed electron beam. FIG. 4 illustrates a schematic configuration of a modified pulsed electron beam radiation apparatus including electrically isolated metal plates that contain the target material. The target material is sputtered from the metal plates, and can be micro-alloyed onto the metallic glass surface.

The modified apparatus 400 can be used for sputtering a target material onto the surface of the metallic glass and micro-alloying the target material with the metallic glass and forming an amorphous surface region. Apparatus 400 includes a pulsed electron beam radiation apparatus 410 as an electron source and also electrically isolated metal plates 416A-B, which may be positioned on opposite sides of an electron beam 420 that is outputted from the pulsed electron beam radiation apparatus 410. The metal plates 416A-B and the electron beam 420 can all be contained within a vacuum chamber (not shown). The metal plates 416 may be formed of a target material, such as copper among other metals. The metal plates 416 must be electrically isolated to keep the electron beam 420 scattering.

Sputtering occurs when the side portions 420A and 420B of the electron beam 420 hit the target materials on both sides of the electron beam. Sputtering is a process for ejecting atoms from a solid target material by bombardment of the target by energetic particles. Sputtering can deposit a layer of the target material onto the specimen 424, which is placed inside the vacuum chamber (not shown). The specimen 424 may be a metallic glass.

When the electron beam 420 hits the metal plates 416, atoms or ions of the target material are knocked out, referred to as sputtered atoms. Sputtered atoms or ions may be scattered to the surface 406 of a metallic glass to form sputtered zones 408A and 408B, respectively, on the surface 406. The middle portion 420C of the electron beam 420 reaches the inner surface region 404 inside the sputtered zones or regions 408A and 408B. In the sputtered regions 408A and 408B, micro-alloying of the target material with the metallic glass occurs such that the surface composition is slightly different from the metallic glass.

In the sputtered zones 408A and 408B, an incoming portion of the electron beam 420 and the sputtered atoms or ions reach the surface of the metallic glass 424 simultaneously. As such, the electron beam 420 causes melting of the metallic glass and micro-alloying of the sputtered atoms or ions with the metallic glass 424 in the sputtered zone.

Also, an electron beam 420 radiating through an aperture 112 of the pulsed electron beam radiation apparatus 410 can be in a three-dimensional (3D) cone shape. Therefore, the beam size or diameter 414 near the metal plates 416A-B can be controlled by varying the distance 412A between the metal plates 416A-B and the aperture 112. The metal plates include the target material, such as copper, aluminum, among others.

The locations of the sputtered regions 408A and 408B can be controlled by adjusting the distance 418 between two metal plates 416A and 416B and the distance 412B from the surface of the metallic glass 424.

Methods of Rejuvenating Surfaces of Metallic Glasses using Electron Beam Radiation

Crystals on the surface of the metallic glass are not desirable. The pulsed electron beam radiation can be used for healing inclusions, e.g. crystals with high melting temperatures. For example, an electronic case or cover may be formed of a metallic glass. When crystals appear on the outer surface of an electronic case, the crystals can detract from the cosmetic appeal of the electronic case. Also, the inner surface of the electronic case may need to have a very good control of the geometric dimensions, such that all the components can fit tightly inside the electronic case.

In some embodiments, rejuvenation of a surface of a localized crystalline portion of a metallic glass by electron beam radiation may repair the surface of a metallic glass having localized regions of crystallization. For example, localized crystalline regions or zones in a metallic glass sample may be treated with an electron beam to transform localized crystalline regions into an amorphous structure. For example, an embrittled sample can be healed by the pulsed electron beam radiation using the apparatus as shown in FIG. 3. By using electron beam radiation, a portion of the crystalline metal portion in a metallic glass can be rejuvenated (i.e. the morphology changed to amorphous).

The method for surface modification of a metallic glass may include selecting an energy band for an electron beam from an electron source. The method may also include applying the electron beam to a surface of a metallic glass having localized regions of crystallization and repairing the surface to change the morphology the localized crystalized regions to become amorphous via the electron beam radiation. In various aspects, the energy band is designed to heat the metallic glass to a temperature below the melting temperature of the metallic glass. The melting temperature of the metallic glass can depend on the alloy, and can be known for a particular metallic glass, or can be determined as known to those skilled in the art.

In some embodiments, rejuvenation of the surface of the metallic glass by electron beam radiation may produce a rejuvenated amorphous region with a depth up to about 100 μm. In some embodiments, the depth may be less than 90 μm. In some embodiments, the depth may be less than 80 μm. In some embodiments, the depth may be less than 70 μm. In some embodiments, the depth may be less than 60 μm. In some embodiments, the depth may be less than 50 μm. In some embodiments, the depth may be less than 40 μm. In some embodiments, the depth may be less than 30 μm. In some embodiments, the depth may be less than 20 μm. In some embodiments, the depth may be greater than 10 μm. In some embodiments, the depth may be greater than 20 μm. In some embodiments, the depth may be greater than 30 μm. In some embodiments, the depth may be greater than 40 μm. In some embodiments, the depth may be greater than 50 μm. In some embodiments, the depth may be greater than 60 μm. In some embodiments, the depth may be greater than 70 μm. In some embodiments, the depth may be greater than 80 μm. In some embodiments, the depth may be greater than 90 μm. In some embodiments, the depth may be greater than 100 μm.

The method for surface modification of a metallic glass may include selecting an energy band for an electron beam from an electron source. The method may also include applying the electron beam to a surface of a crystalline metal portion in a metallic glass. The method may further include rejuvenating the surface to form a surface zone of the crystalized metallic glass, wherein the surface zone becomes amorphous after the electron beam radiation, while a bulk region under the surface zone remains crystalline after the electron beam radiation.

In other embodiments, the methods and apparatus can be used to rejuvenate a portion of a crystalline metal portion in a metallic glass. For example, FIG. 6B illustrates a rejuvenated metallic glass layer on a crystalline metal portion in a Zr-based metallic glass in an embodiment. As shown in FIG. 6B, a metallic glass layer 606 is formed on the crystalline metal portion of a metallic glass 608 by the pulsed electron beam radiation using the modified pulsed electron beam radiation apparatus 300. The rejuvenation is facilitated by controlling the energy of the electron beam via the electron beam apparatus 300, as described above. The rejuvenated metallic glass layer 606 is can be about 100 μm thick. In some aspects, the rejuvenated metallic glass layer is at least 50 μm thick. In some aspects, the rejuvenated metallic glass layer is at least 150 μm thick. In some aspects, the rejuvenated metallic glass layer is at least 250 μm thick. In some aspects, the rejuvenated metallic glass layer is at least 350 μm thick.

Rejuvenation occurs by electron penetration into the metallic glass, causing the crystalline metal portion in a metallic glass to change to an amorphous phase without melting the metallic glass. This process differs from micro-alloying. The average energy may vary with the metallic glass and would be low enough in order not to melt the surface of the metallic glass, but only rejuvenate the surface of the crystalline metal portion in the metallic glass. The electron beam of a pulsed electron beam may have an average energy lower than that used for micro-alloying.

As demonstrated herein, the electrons may have high enough energy to melt the surface of the metallic glass and to allow the metallic glass to micro-alloy with other target elements. FIG. 7A is a schematic that illustrates an amorphous structure having a surface melted by an electron beam in an embodiment. As shown in FIG. 7A, an electron beam 702 radiates toward a surface area 704 of an amorphous structure or a metallic glass 706. A temperature rise occurs near the surface area 704 to form a thin temperature rise region 708, for example, having a thickness of about a few microns, e.g. 2-3 μm. In the temperature rise region 708, the temperature may rise to be above the melting temperature of the metallic glass. Micro-alloying can occur in the melted surface region 708.

FIG. 7B is a schematic that illustrates the surface modification or rejuvenation of a crystalline metal portion in a metallic glass by the electron beam radiation. The surface temperature rises as a result of the electron beam radiation. A portion of the electron beam 702 penetrates through the temperature rise region 708. As such, the penetrated electron beam can change the atoms of the crystalline metal portion in the metallic glass 706 to become an amorphous phase and to form a rejuvenated amorphous region 710 from the surface 704. The rejuvenated amorphous region 710 has a depth of up to 100 μm. The electron beam radiation modifies the surface region of the crystalline metal portion in the metallic glass, but does not affect the bulk of the crystalline metal portion in the metallic glass that extends beyond the rejuvenated amorphous region 710. A large flux of the electron beam may be used to enhance the depth of rejuvenated amorphous region 710. The energy level for the electron beam radiation may be different from that used for micro-alloying.

In order to identify the structure of the rejuvenated surface as shown in FIG. 6B, X-ray diffractometry was used for analysis. FIG. 8A is an X-ray diffraction pattern for a crystalline metal portion in a metallic glass prior to rejuvenation in an embodiment. An X-ray diffraction pattern 800A of the crystalline metal portion in the metallic glass before the electron beam radiation includes two major peaks 802, which indicate a β₂ crystalline phase with a composition similar to a nominal composition.

FIG. 8B is an X-ray diffraction pattern for a crystalline metal portion in a metallic glass of FIG. 8A after rejuvenation in an embodiment. An X-ray diffraction pattern 800B of the metallic glass after the electron beam radiation includes a broad peak 804, which indicates an amorphous phase.

The composition of the rejuvenated surface region remains unchanged, because no diffusion of elements occurs during the healing process of a crystalline metal portion in a metallic glass when healing a crystalline metal portion in a metallic glass by using an electron beam radiation apparatus 300 having a controlled energy to form a rejuvenated amorphous structure with a depth of up to 100 μm. Diffusion refers to a process where two different material surfaces are in contact, upon the application of sufficient energy, and atoms from one material move into the other material through the interface, resulting in an intermediate region that includes alloys formed by the two materials as a result of the diffusion.

FIG. 9 is an optical image of a crystalline metal portion in a metallic glass prior to rejuvenation by pulsed electron beam radiation in an embodiment. The metallic glass is crystallized, including a crystalline metal portion in a metallic glass 904 and a surface layer 902. It appears that the surface layer 902 has embrittlement, such that the surface layer 902 includes a crystalline portion, and appears slightly different from the metallic glass 904 prior to electron beam radiation.

FIG. 10 is an optical image of a crystalline metal portion in a metallic glass after rejuvenation by pulsed electron beam radiation in an embodiment. As shown in FIG. 10, a surface layer 1002 of a metallic glass substrate 1004 is rejuvenated by the pulsed electron beam radiation using the apparatus 300 to form a rejuvenated amorphous structure having a depth of about 60 μm, which is less than that shown in FIG. 6B. The bulk of the metallic glass 1004 still remains crystallized, and only the surface region becomes an amorphous structure without any change in its composition. Also, as shown in FIG. 10, the amorphous layer 1002 is homogeneous, which may be better than a partially melted region from a welding, which causes non-homogeneousness to the surface.

Methods of Micro-alloying Metallic Glasses using Electron Beam Radiation

In other embodiments, the disclosure is directed to methods of using electron beam radiation to micro-alloy metallic glasses. The mechanisms for micro-alloying and rejuvenation are different. Micro-alloying occurs in the surface melt region of the metallic glass, while rejuvenation occurs by penetrating electrons into the metallic glass and causing a crystalline metal portion in a metallic glass to change to an amorphous phase, as explained above.

Micro-alloying of metallic glasses can be achieved by placing a target material, such as Cu, Al, etc., at an intermediate position between an electron beam gun or source and a specimen, as shown in FIG. 4. The micro-alloying technique can form an amorphous surface region with a depth of up to a few microns on the metallic glass. In some embodiments, the surface zone has a depth of up to 10 μm. In some embodiments, the surface zone has a depth of up to 5 μm. In some embodiments, the surface zone has a depth of up to 4 μm. In some embodiments, the surface zone has a depth of up to 3 μm. In some embodiments, the surface zone has a depth of up to 2 μm. In some embodiments, the surface zone has a depth of up to 1 μm. The surface zone has a slightly different composition from the metallic glass.

The electron beam is a pulsed electron beam. The average energy may vary with the metallic glass and would be high enough to melt the surface of the metallic glass to alloy micro-alloying with the target material. The electron beam may have an energy band width sufficient to heat the alloy at or above its melting point. The melting point of the alloy can readily be determined by those skilled in the art.

Generally, the method includes placing a pair of metal plates between an electron beam source and a surface of a metallic glass, the metal plates including a target material. The method also includes sputtering the target material from the metal plates on the surface of the metallic glass. The method further includes micro-alloying the target material with the metallic glass and forming an amorphous surface zone.

FIG. 5 shows the trial data of copper (Cu) sputtered on a Zr-based bulk metallic glass (BMG). A ring region 504 is formed on a metallic glass 502. The ring region 504 is a Cu sputtered region. The atoms or ions from the target material may be knocked out by the electron beam radiation to generate sputtered atoms or ions, which are scattered onto a surface of the metallic glass. The sputtered atoms or ions can be micro-alloyed with the metallic glass on the surface by using the pulsed electron beam radiation. After oxidization, the Cu sputtered region 504 changes color to become darker. This color change can be caused by micro-alloying of Cu with the metallic glass.

The effect of micro-alloying on the metallic glass by pulsed electron beam radiation was examined. FIG. 6A illustrates a micro-alloyed surface of a Zr-based metallic glass with Cu in an embodiment. The micro-alloyed region on the metallic glass may be a few microns thick. The surface composition can be controlled by micro-alloying of a target material with the metallic glass by using the modified pulsed electron beam radiation apparatus 400. As shown, a copper layer of about 0.5 μm thick was sputtered or plated on a Zr-based bulk metallic glass. The depth of the melted region of FIG. 6A may be from about 3 μm to 5 μm. Therefore, the micro-alloyed region may be about 2 μm thick. In this micro-alloyed region, the Zr-based metallic glass is micro-alloyed with Cu. Outside the micro-alloyed region, the Zr-based metallic glass remains unchanged. The conditions for the pulsed electron beam include an acceleration voltage, which controls the electron kinetic energy. Radiation energy can depend upon both density of electrons and kinetic energy of the electrons. Kinetic energy plays an important role in affecting the surface modification. The kinetic energy seems an important factor to control the surface condition.

In some embodiments, the acceleration voltage may be at least 1 kV. In some embodiments, the acceleration voltage may be greater than 2 kV. In some embodiments, the acceleration voltage may be greater than 5 kV. In some embodiments, the acceleration voltage may be greater than 10 kV. In some embodiments, the acceleration voltage may be greater than 15 kV. In some embodiments, the acceleration voltage may be greater than 20 kV. In some embodiments, the acceleration voltage may be greater than 25 kV. In some embodiments, the acceleration voltage may be greater than 30 kV. In some embodiments, the acceleration voltage may be less than 35 kV. In some embodiments, the acceleration voltage may be less than 30 kV. In some embodiments, the acceleration voltage may be less than 25 kV. In some embodiments, the acceleration voltage may be less than 20 kV. In some embodiments, the acceleration voltage may be less than 15 kV. In some embodiments, the acceleration voltage may be less than 10 kV. In some embodiments, the acceleration voltage may be less than 5 kV.

The conditions for the pulsed electron beam may also include an argon plasma with a pressure of at least 0.01 Pa. In some embodiments, the pressure may be greater than 0.02 Pa. In some embodiments, the pressure may be greater than 0.03 Pa. In some embodiments, the pressure may be greater than 0.04 Pa. In some embodiments, the pressure may be greater than 0.05 Pa. In some embodiments, the pressure may be greater than 0.06 Pa. In some embodiments, the pressure may be greater than 0.07 Pa. In some embodiments, the pressure may be greater than 0.08 Pa. In some embodiments, the pressure may be greater than 0.09 Pa. In some embodiments, the pressure may be greater than 0.10 Pa. In some embodiments, the pressure may be greater than 0.11 Pa. In some embodiments, the pressure may be greater than 0.12 Pa. In some embodiments, the pressure may be greater than 0.13 Pa. In some embodiments, the pressure may be greater than 0.14 Pa. In some embodiments, the pressure may be less than 0.15 Pa. In some embodiments, the pressure may be less than 0.14 Pa. In some embodiments, the pressure may be less than 0.13 Pa. In some embodiments, the pressure may be less than 0.12 Pa. In some embodiments, the pressure may be less than 0.11 Pa. In some embodiments, the pressure may be less than 0.10 Pa. In some embodiments, the pressure may be less than 0.09 Pa. In some embodiments, the pressure may be less than 0.08 Pa. In some embodiments, the pressure may be less than 0.07 Pa. In some embodiments, the pressure may be less than 0.06 Pa. In some embodiments, the pressure may be less than 0.05 Pa. In some embodiments, the pressure may be less than 0.04 Pa. In some embodiments, the pressure may be less than 0.03 Pa. In some embodiments, the pressure may be less than 0.02 Pa.

The conditions for the pulsed electron beam may also include a solenoid coil voltage. In some embodiments, the coil voltage may be greater than 0.1 kV. In some embodiments, the coil voltage may be greater than 0.2 kV. In some embodiments, the coil voltage may be greater than 0.3 kV. In some embodiments, the coil voltage may be greater than 0.4 kV. In some embodiments, the coil voltage may be greater than 0.5 kV. In some embodiments, the coil voltage may be greater than 0.6 kV. In some embodiments, the coil voltage may be greater than 0.7 kV. In some embodiments, the coil voltage may be greater than 0.8 kV. In some embodiments, the coil voltage may be greater than 0.9 kV. In some embodiments, the coil voltage may be greater than 1.0 kV. In some embodiments, the coil voltage may be greater than 1.1 kV. In some embodiments, the coil voltage may be greater than 1.2 kV. In some embodiments, the coil voltage may be greater than 1.3 kV. In some embodiments, the coil voltage may be greater than 1.4 kV. In some embodiments, the coil voltage may be greater than 1.5 kV. In some embodiments, the coil voltage may be greater than 1.6 kV. In some embodiments, the coil voltage may be greater than 1.7 kV. In some embodiments, the coil voltage may be greater than 1.8 kV. In some embodiments, the coil voltage may be greater than 1.9 kV. In some embodiments, the coil voltage may be less than 2.0 kV. In some embodiments, the coil voltage may be less than 1.9 kV. In some embodiments, the coil voltage may be less than 1.8 kV. In some embodiments, the coil voltage may be less than 1.7 kV. In some embodiments, the coil voltage may be less than 1.6 kV. In some embodiments, the coil voltage may be less than 1.5 kV. In some embodiments, the coil voltage may be less than 1.4 kV. In some embodiments, the coil voltage may be less than 1.3 kV. In some embodiments, the coil voltage may be less than 1.2 kV. In some embodiments, the coil voltage may be less than 1.1 kV. In some embodiments, the coil voltage may be less than 1.0 kV. In some embodiments, the coil voltage may be less than 0.9 kV. In some embodiments, the coil voltage may be less than 0.8 kV. In some embodiments, the coil voltage may be less than 0.7 kV. In some embodiments, the coil voltage may be less than 0.6 kV. In some embodiments, the coil voltage may be less than 0.5 kV. In some embodiments, the coil voltage may be less than 0.4 kV. In some embodiments, the coil voltage may be less than 0.3 kV. In some embodiments, the coil voltage may be less than 0.2 kV.

In summary, the disclosure provides a pulsed electron beam radiation apparatus including a filter that can remove the extra high energy electrons and control the energy of the electron beams. The pulsed electron beam radiation apparatus can be used for healing a surface having structural relaxation or embrittlement, such as a metallic glass that is crystallized.

In other embodiments, the apparatus can also include adding a pair of electrically isolated metal plates that are placed between the pulsed electron beam source and the specimen to be treated. The metal plates include a target material, which can be sputtered onto the surface for micro-alloying the surface of the metallic glass. This micro-alloying technique can be used for adding an oxide layer on the metallic glass to change the color, wear resistance, or corrosion resistance, among other applications.

In some embodiments, for an as-cast bulk amorphous structure or bulk metallic glass, the surface of the as-cast bulk amorphous structure can be treated by the pulsed electron beam radiation to avoid cracking originating from the surface of the amorphous structure.

The systems and methods described herein can be applicable to any suitable metallic glass known in the art. In some non-limiting aspects, the metallic glass can be based on, or alternatively include, one or more elements that oxidize, such as Zr, Ti, Ta, Hf, Mo, W, and Nb. In some variations, the metallic glass includes at least about 30% of one or more of Zr, Ti, Ta, Hf, Mo, W, and Nb. In some variations, the metallic glass includes at least about 40% of one or more of Zr, Ti, Ta, Hf, Mo, W, and Nb. In some variations, the metallic glass includes at least about 50% of one or more of Zr, Ti, Ta, Hf, Mo, W, and Nb. In certain embodiments, the metallic glass can be based on, or alternatively include, Zr. In some variations, the metallic glass includes at least about 30% Zr. In some variations, the metallic glass includes at least about 40% Zr. In some variations, the metallic glass includes at least about 50% Zr. Similarly, the surface treated metallic glass material described herein as a constituent of a composition or article can be of any type.

As used herein, the terms including metallic glass, metallic glass alloy, amorphous metal, amorphous alloy, bulk metallic glass, and BMG are used interchangeably.

The metallic glass can include multiple transition metal elements, such as at least two, at least three, at least four, or more, transitional metal elements. The metallic glass can also optionally include one or more nonmetal elements, such as one, at least two, at least three, at least four, or more, nonmetal elements. A transition metal element can be any of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, rutherfordium, dubnium, seaborgium, bohrium, hassium, meitnerium, ununnilium, unununium, and ununbium. In one embodiment, a BMG containing a transition metal element can have at least one of Sc, Y, La, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, and Hg. Depending on the application, any suitable transitional metal elements, or their combinations, can be used.

Depending on the application, any suitable nonmetal elements, or their combinations, can be used. A nonmetal element can be any element that is found in Groups 13-17 in the Periodic Table. For example, a nonmetal element can be any one of F, CI, Br, I, At, O, S, Se, Te, Po, N, P, As, Sb, Bi, C, Si, Ge, Sn, Pb, and B. Occasionally, a nonmetal element can also refer to certain metalloids (e.g., B, Si, Ge, As, Sb, Te, and Po) in Groups 13-17. In one embodiment, the nonmetal elements can include B, Si, C, P, or combinations thereof. Accordingly, for example, the alloy can include a boride, a carbide, or both.

In some embodiments, the metallic glass described herein can be fully alloyed. The term fully alloyed as used herein can account for minor variations within the error tolerance. For example, it can refer to at least 90% alloyed, such as at least 95% alloyed, such as at least 99% alloyed, such as at least 99.5% alloyed, or such as at least 99.9% alloyed. The percentage herein can refer to either volume percent or weight percentage, depending on the context. These percentages can be balanced by impurities, which can be in terms of composition or phases that are not a part of the alloy. The alloys can be homogeneous or heterogeneous, e.g., in composition, distribution of elements, amorphicity/crystallinity, etc.

The metallic glass can include any combination of the above elements in its chemical formula or chemical composition. The elements can be present at different weight or volume percentages. Alternatively, in one embodiment, the above-described percentages can be volume percentages, instead of weight percentages.

In certain embodiments, the metallic glass can be zirconium-based. The metallic glass can also be substantially free of various elements to suit a particular purpose. For example, in some embodiments, the metallic glass can be substantially free of nickel, aluminum, titanium, beryllium, or combinations thereof. In one embodiment, the alloy or the composite is completely free of nickel, aluminum, titanium, beryllium, or combinations thereof.

The metallic glasses can further include additional elements, such as additional transition metal elements, including Nb, Cr, V, and Co. The additional elements can be present at less than or equal to about 30 wt %, less than or equal to about 20 wt %, less than or equal to about 10 wt %, or less than or equal to about 5 wt %. In one embodiment, the additional, optional element is at least one of cobalt, manganese, zirconium, tantalum, niobium, tungsten, yttrium, titanium, vanadium and hafnium to form carbides and further improve wear and corrosion resistance. Further optional elements may include phosphorous, germanium and arsenic, totaling up to about 2%, and preferably less than 1%, to reduce the melting point. Otherwise incidental impurities should be less than about 2% and preferably 0.5%.

In some embodiments, the metallic glass can include a small amount of impurities. The impurity elements can be intentionally added to modify the properties of the composition, such as improving the mechanical properties (e.g., hardness, strength, fracture mechanism, etc.) and/or improving the corrosion resistance. Alternatively, the impurities can be present as inevitable, incidental impurities, such as those obtained as a byproduct of processing and manufacturing. The impurities can be less than or equal to about 10 wt %, about 5 wt %, about 2 wt %, about 1 wt %, about 0.5 wt %, or about 0.1 wt %. In some embodiments, these percentages can be volume percentages instead of weight percentages.

The methods of modifying the surface of a metallic glass, methods of micro-alloying, and methods of changing crystalline metal portions in a metallic glass surface can be used in any metal-containing device known in the art. FIG. 11 depicts a portable electronic device 1100. The metal substrate that makes up housing 1102 can be modified as described herein. In various aspects, the metallic glass can be rejuvenated using lower energy electron beams. In some aspects, a localized crystalline metal portion within a metallic glass can be rejuvenated to form an amorphous structure. Any portion of an electronic device, including housings, can be formed or altered in any manner as described herein.

The methods and apparatus disclosed herein can be valuable in the fabrication of electronic devices using a metallic glass-containing part. An electronic device herein can refer to any electronic device known in the art. For example, it can be a telephone, such as a mobile phone, and a land-line phone, or any communication device, such as a smart phone, including, for example an iPhone®, a watch, for example and AppleWatch®, and an electronic email sending/receiving device. It can be a part of a display, such as a digital display, a TV monitor, an electronic-book reader, a portable web-browser (e.g., iPad®), and a computer monitor. It can also be an entertainment device, including a portable DVD player, conventional DVD player, Blue-Ray disk player, video game console, music player, such as a portable music player (e.g., iPod®), etc. It can also be a part of a device that provides control, such as controlling the streaming of images, videos, sounds (e.g., Apple TV®), or it can be a remote control for an electronic device. It can be a part of a computer or its accessories, such as the hard drive tower housing or casing, laptop housing, laptop keyboard, laptop track pad, desktop keyboard, mouse, and speaker. The article can also be applied to a device such as a watch or a clock.

The methods can also be valuable in forming wearable metallic glass products that have a good cosmetic profile and do not readily degrade or show evidence of wear.

Any ranges cited herein are inclusive. The terms “substantially” and “about” used throughout this Specification are used to describe and account for small fluctuations. For example, they can refer to less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%.

Having described several embodiments, it will be recognized by those skilled in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention.

Those skilled in the art will appreciate that the presently disclosed embodiments teach by way of example and not by limitation. Therefore, the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall there between. 

What is claimed is:
 1. A method of modifying a crystalline metal portion in a metallic glass comprising: applying an electron beam within an energy band to the crystalline metal portion at a surface zone of the metallic glass; and changing the crystalline metal portion to an amorphous portion at the surface zone of the metallic glass, while a bulk metal region embedded in the metallic glass under the surface zone remains crystalline.
 2. The method of claim 1, wherein the surface zone has a depth up to 100 μm.
 3. The method of claim 1, further comprising selecting the energy band of the electron beam by filtering out electrons having energy above an upper threshold energy.
 4. The method of claim 3, comprising filtering out the electrons having energy below a lower threshold energy.
 5. The method of claim 1, wherein the electron beam is a pulsed electron beam.
 6. The method of claim 1, wherein the surface zone has the same chemical composition as the bulk region.
 7. The method of claim 1, wherein the metallic glass is selected from a group consisting of a Zr-based metallic glass, a Pt-based metallic glass, a Pd-based metallic glass, a Au-based metallic glass, a Ag-based metallic glass, a Ni-based metallic glass, and a Fe-based metallic glass.
 8. A method of micro-alloying an element on a metallic glass comprising: placing a target material onto a portion of a surface of the metallic glass; and alloying the target material with the metallic glass to form an amorphous surface zone with a depth of up to 5 μm in the metallic glass.
 9. The method of claim 8, wherein the amorphous surface zone has a different composition from the metallic glass.
 10. The method of claim 8, wherein the target material comprises copper.
 11. The method of claim 8, wherein the metallic glass comprises a Zr-based metallic glass, a Pt-based metallic glass, a Pd-based metallic glass, a Au-based metallic glass, a Ag-based metallic glass, a Ni-based metallic glass, and a Fe-based metallic glass.
 12. The method of claim 8, further comprising applying an electron beam to the surface of the metallic glass, before alloying the target material.
 13. The method of claim 12, wherein the electron beam is a pulsed electron beam.
 14. A method of modifying a surface of a metallic glass comprising: applying an electron beam to a localized crystalline metal portion at the surface of the metallic glass to heat the metallic glass at a temperature below the melting temperature of the metallic glass; and rejuvenating the localized crystalline metal portion into an amorphous portion.
 15. The method of claim 14, wherein the amorphous portion has a depth of up to 100 μm.
 16. A metal comprising a metallic coating diffused into a surface of a metallic glass substrate to a depth of at least 50 microns.
 17. The metal according to claim 16, wherein the metallic coating is diffused into the metallic glass substrate to a depth of at least 75 microns.
 18. The metal according to claim 16, wherein the metallic coating is diffused into the metallic glass substrate to a depth of at least 90 microns.
 19. A metal comprising a metallic coating diffused into a metallic glass substrate to a depth up to 5 microns.
 20. An electronic device comprising a housing, the housing comprising the metal according to claim
 19. 